The present invention relates generally to a baffle in a clarifier tank for gravitationally separating solids suspended in a liquid contained in the tank. These baffle devices are also known in the art as a lamella gravity separator or settler. The clarifiers with which the inventive baffle device is used typically have a circular or rectangularly-configured tank in which a centrally mounted, radially-extended arm is slowly moved or rotated about the tank at or proximate to the surface of the carrier liquid. For a more detailed description of such vented (and non-vented) baffle systems, U.S. Pat. Nos. 5,252,205 and 5,597,483 to Schaller are referred to and hereby incorporated by reference.
Typical prior art vented baffles such as that shown in FIG. 1, that are mounted in cantilevered fashion along a peripheral wall of the clarifier intermediate with respect to the tank bottom and the surface of the carrier liquid contained in the tank. The vented baffle system includes a plurality of such baffles which are constructed as modular units and form a continuous, single-surface sheet that slopes downwardly from the peripheral tank wall toward the center of the tank and terminates at a free edge suspended spaced apart and above the tank bottom. More specifically, each panel member which is downwardly sloping from the peripheral tank wall toward the interior of the tank and the tank bottom, is provided with a lower side and an upper side. The panel member extends downwardly from an upper edge secured to the peripheral tank wall to a lower edge disposed in a spaced relation to the tank bottom. The panel member has a first lateral side and a second lateral side with the panel member defining a space formed between the junction of the lower side of the panel member and the peripheral tank wall.
Due to the inclined configuration of these baffles, air may be trapped during the filling of the tank in a space formed between the junction of the lower side of the panel member and the peripheral tank wall. Other gases that may form naturally as a part of the process which takes place within the clarifier, may also be trapped in this space. Accordingly, the forces imposed by these gases on the baffle require that the baffle be constructed and mounted in such a manner that will withstand these forces. As well, the build-up of pressure from these gases can be extreme with damage to the baffle unit or clarifier resulting unless some form of venting is provided.
A common form of prior art venting (not shown) relies on one or more holes drilled in the baffle panel member to continually vent the gas to the surface and alleviate the build-up of pressure. Small holes (1 inch diameter or less) however rapidly become clogged with sludge and become ineffective. Larger holes allow the continual up-flow of waste solids and can create a negative impact on the performance of the baffle.
Numerous clarifier and baffle configurations are disclosed in the art. However, prior art attempts have suffered from a variety of various drawbacks and deficiencies.
For example, U.S. Pat. No. 4,109,433 to Maze relates to a ventilator for spaces under slanted roofs or attics such as a gable, hip and shed roof types. Specifically, the ventilator uses an elongate duct positioned between the adjacent rafters under a roof. However, there is no disclosure in the reference of an improved vented baffle system which is constructed as a modular unit and that consists of a plurality of inter-engaged individual baffles, each formed as a unitarily-integrated element incorporating the panel member, a vent means and an integral end bracket for suspended securement of the baffle to the peripheral wall of the clarifier tank.
U.S. Pat. No. 5,286,392 to Shea is directed to a launder and baffle structure used in association with a filtration tank of which the type using granular filtration media is disclosed. Specifically, a regulable air discharge system is disclosed to release a selected amount of air from beneath the baffle system in order to regulate turbulence and thereby facilitate quiescence of flow. This reference, however, does not teach an improved vented baffle system having a plurality of baffles with each baffle consisting of unitarily-integrated design incorporating a panel member, an end bracket for cantilevered securement of the baffle to the peripheral wall and a relief valve means which is in fluid communication with the space formed between the junction of the lower side of the panel member and the peripheral tank wall preventing the pressure in said space.
Another prior art arrangement provides for vented baffles extending in an upward fashion projecting upwards as shown in FIG. 1 taken from U.S. Pat. No. 5,597,483. In such wastewater treatment facilities utilizing secondary clarifiers, the clarifier's effectiveness in removing solids is one of the most important factors in establishing the final effluent quality of the facility. A major deterrent to effective removal is the presence of sludge density currents that cause hydraulic short circuits within the tank. These short circuits, in turn, allow solids concentrations to unintentionally bypass the tank's clarification volume and enter the effluent.
In prior art upwardly vented baffles such as the one shown in FIG. 1, the vent is typically a hole or half-round vertical duct of various size drilled or molded into the top of the inclined surface of the baffle. These vents release gases that accumulate underneath the baffle. The gases are a result of the decomposition of the solids within the dense sludge blanket below and the solids that float and gather up under the baffle panels. This occurrence is part of every clarifier due to the composition of the water that resides within them. The vents not only allow the gases to pass but they also allow water to flow through. The water will also have solids in it but typically not enough to impede on the performance of the baffle.
However, in the cases of where there is a heavy concentration of solids or higher water flow causing the water to be more concentrated, the water flow through the upwardly directed vent can diminish the performance of the baffle by increasing the Total Suspended Solids (TSS) concentration of the water going over the weir as the vents direct the solids and gas directly up along the outer wall of the tank towards the weir and spill channel.